Hitherto, for determination of the demagnetization loss state of a permanent magnet constituting a vehicle drive motor such as an IPM motor, the demagnetization loss state or the residual magnetic flux density in a magnet has been determined based on the value obtained by reading the magnetic flux density at a desired site on the surface of the magnet by a gaussmeter or the like. In addition, Patent Document 1 discloses a magnetometer that can be used for magnetometry of a relatively large magnet.
As an aside, when a permanent magnet is actually examined, it is needless to say that the magnetization state in the magnet (e.g., the demagnetization loss state or the residual magnetic flux density) varies for each portion of the permanent magnet. Further, for so-called coercivity distribution magnets, coercivity is an important magnet performance factor, in addition to the magnetic flux density. Also, such a coercivity distribution magnet literally has a distribution in which coercivity varies for each portion.
In view of quality assurance of coercivity distribution magnets, it is very important to determine such coercivity distribution in a coercivity distribution magnet (i.e., coercivity of an arbitrary portion in the magnet) with good accuracy.
For instance, in one case, an optimum design is created for a coercivity distribution magnet to be embedded in an IPM motor rotor as described above such that magnetic properties of a portion of the lateral face of the magnet on the stator side are relatively improved based on the magnetic flux from the stator side.
In such case, it is very important to determine coercivity of each portion in a coercivity distribution magnet with good accuracy before the start of the in-service period or in one phase after the start of the in-service period so as to assure the quality of each desired portion of the coercivity distribution magnet to be examined with good accuracy not only for the future magnet development but also for the credibility of magnet manufacturers and manufacturers using magnets.
However, at present, a method comprising cutting a coercivity distribution magnet into pieces and determining the coercivity of each piece is merely used.
Therefore, instead of conventional coercivity determination methods wherein a coercivity distribution magnet is cut into pieces for determination of coercivity of each piece, useful methods for determining a coercivity distribution and coercivity of an arbitrary position in the magnet with good accuracy without cutting the magnet into pieces have been sought in the art.    Patent Document 1: JP Patent Publication (Kokai) No. 2006-64419 A